In any inkjet system, the ink goes through various physical and geometric constraints which influence the flow dynamics and finally the jetting characteristics. The dynamic flow behaviour in-channel, through the nozzle and in flight during printing is vital to control print quality (drop ejection characteristic, reliability) and further advances in the capability of inkjet technology.This paper will discuss the flow behaviour at each stage of a drop-on-demand printhead. The fluid dynamics of the ink on the millimetre scale within the printhead inlet is very different to that on the micron scale within the channel and nozzle. Although they are all in the laminar flow regime they are subject to very different shear rates. In a printhead, various system components (ink, heaters, pumps, actuator and nozzle) must be designed or configured to achieve target velocity, frequency, drop size, and reliability. Both simulation and experimental results on these topics will be discussed in this paper.